Thermal cut-out device



Dec. 28 1926. 1,612,246

G. H. WHITTINGHAM THERMAL CUT-- OUT DEVI CE o i Filed August 3, 1920 Patented Dec. 28, 1926.

UNITED STATES GEORGE E. wm'm'mdm, or

PATENT OFFICE.

BALTIMORE, MARYLAND, ASSIGNOR TO MONITOR LAND.

THERMAL CUT-OUT DEVICE.

Application filed August 3,1920, Serial :0. 401,051. Renewed November as, 1925.

This invention devices, adapted articularly for causing an interruption of t e armature circuit ofan electric motor upon the occurrencevof 'prolonged overload. The device however, may be used for other purposes. In carrying out the invention,'I provide a closed chamber, containing an expansible fluid, preferably a volatile liquid, such as ether, and having a metal wall adapted to expand and contract according to variations in the ressure of the fluid within the chambcnhe expansible Wall of this chamber is included inthe electric circuit and is relatively thin, so that it will heat with the passage of an excessive current. The wall thus constitutes an electric heating element for the fluid within the chamber, and the wall of the chamber expands and contracts in accordance with the 2 variations in the fluid pressure caused by the heat generated by the electric current.

In the accompanying drawing,

1 shows in side elevation, partly broken away, a circuit controlling device embodying my improvements, the circuits of an electric motor being shown connected thereto for the purpose of illustrating the opera tion;

Fig. 2 is a central, longitudinal section so through a modified form of circuit controlling device; and,

Fig. 3 is a section on Fig. 2.

BGfOTTlllg to Fig, l of the drawing, A 'indicates a closed chamber, comprising a "transversely corrugated metal tube, the wall. of which is relatively thin, and also exipansible longitudinally to considerable entent by reason ot the corrugations, @ne end st of the tube is closed by a metal plug l, which is supported a bracket 2, and to said plug is secured terminal 3, adapted for connection to an electric circuit, The other end of the tube is closed by a metal plug 4,

the line 3-3 of to which is attached a rod 5, which slides through an opening in a suitable guide 6 and engages slot in a pivoted switch arm 7. A terminal 8 is connected to the plug 4 by suitable means, such as the nut 9 threaded on the rod 5.

relates to thermal cut-out.

The tube A contains a fluid which, when heated, will expand and by its pressure cause an elongation of the tube. One end of the tube being fixed in the bearing 2, the other end, carrying the rod 5, will move and cause a movement of the switch lever 7 whenthe tube expands or contracts. The wall of the tube forms a part of the electric circuit and is made of relatively thin material so that it will become hot with the passage of an abnormal current through it and it thus constitutes a heating element for the fluid which is within the tube. Thus, the passage of an excessive current through the wall of the tube' causes the generation of heat in the body of the tube.' This in turn, causes an expansion of the fluid and an increase in pressure in the tube, and as a result of the increase in pressure, the tube expands longitudinally and operates the switch arm. Upon reduction in current and consequent cooling of the tube, the fluid cools and the tube contracts, causing a movement of the switch arm in the opposite direction.

For the purpose of illustrating one application of the invention, 1 have shown a simplified diagram of the circuits of an electric motor connected to the cut-out device. In this diagram, M indicates the motor, S indicates an electromagnetically controlled main switchfor opening and closing the field and armature circuits of the motor, and l? indicates a manually controlled switch for closing and opening the circuit of the mag-- net which controls the main switch. The circuit of the motor extends from the line wire L to terminal 3., thence through the wall of the tube A. to terminal 8, thence through conductor 10 to the main stationary contact ll of the switch S, thence through switch arm 12, by conductors 13 and it, to the field and armature, respectively, of the inotor M, and thence by conductor 15 to the supply wire L. The circuit for the magnet 16 of the-main switch extends from the line L, through the tube Am the conductor l0, and thence through conductor 17, push button switch P and conductor 17*. to the coil of the magnet, and thence through conductors 18 and 18 and resistance r to conill THE

ductor 15 and thence to the line wire 1U. When the switch I is closed, the magnet will be energized and will attract the switch arm 12, causing the closure of the main switch, and the motor will start. Vi] hen the switch arm moves to closed position, the arm engages an auxiliary contact 19 and completes a circuit through the magnet 16,- which circuit remains closed after the push button switch P is released and opens. This circuit for the magnet extends from conductor 10, through contact 11 to the switch arm thence tliroughicontact 19 to conductor 1?, thence through the magnet coil to conductor 18, and thence to the line L.

The arm 7, which constitutes one mem ber of a switch T, carries at its free end a contact 20, adapted to engage a stationary adjustable contact 21, andthese contacts are connected to the terminals of the coil of the magnet 16 so that when the contacts 20 and 21 are in engagement, a shunt will be formed around said coil and the magnet will be deenergized, permitting the switch arm 12 to move to open position. As shown, the shunt circuit for the coils of the magnet 1.6 extends from contact 20, through conductors 22 and 17*, to one terminal of the magnet coil and thence through conductors 18* and 23 to the fixed contact 21.

in operation, the switch P is closed momentarily and this causes the magnet to close the main switch and start the motor. The main switch remains closed while the motor is in operation. Should the motor, for any reason, such as an overload, take an excessive amount of current in its armature circuit, this excessive current, which passes through the wall of the tube A, will cause the wall to heat and the consequent heating of the fluid within the tube will give rise to an internal pressure which will expand the tube longitudinally and will cause the closure of the switch T. iii/hen this switch closes, the magnet 16 becomes shortcircuited and the main switch drops open and interrupts the flow of current through the tube and through the motor. lit will be evident that a momentary increase in the armature current will not cause the closure of the switch T, but any prolonged increase of the current through the motor will cause the switch to close and the motor circuit to be interrupted.

Preferably, in order to protect the tube A from drafts, the latter will be enclosed in a tube 24, of heat insulating material, such as asbestos, suitably perforated to permit radiation of heat from the tube.

In Fig. 2 of the drawing, T have shown a modification in which the closed chamber A is composed of a series of thin metal disks a, each having a central opening a (Fig. 3). These disks are arranged in pairs, connected together at their peripheries, and the adjareraaae cent disks of the several pairs are connected at their central openings to metal sleeves (1 The disks are annularly corrugated in order to make them flexible. The entire series of connected disks constitutes a bellows which collapses by reason of the resiliency of its \vallsand which may expand to a considerable extent to operate a switch T, similar to the switch T in Fig. 1. The sleeves a may be of the same metal as the disks, but preferably these sleeves are of a high resistance metal so as to cause heating at the central part of the bellows when an excessive current is passed through it. The bellows,

which is closed airtight at the joints and at the ends, is mounted in the same way as the tube A,-in Fig. 1, and operates the switch T in the same manner. The bellows will be supplied with a suitable quantity of a volatile liquid, before it is closed airtight, and the heating of the bellows by the passage of the current through the disks and particularly through the collars of higher resistance than the disks, willcause vaporization of the liquid and a consequent internal pres sure which will expand the bellows longitudinally. When the current is cut oil, the bellows will contract as the cooling of the bellows and the fluid therein takes place.

The device will operate if the fluid within the closed chamber is simply air or a gas, but in order to insure an extended and for cible expansion of the chamber, I prefer to place within the chamber a suitable quantity of a volatile liquid, such as ether, which will vaporize and, by pressure of the vapor, cause a forcible expansion of the chamber.

What I claim is:

L'The combination with an electric circuit of a closed chamber containing an expansible fluid, said chamber having a cylindrical expansible metal wall included in the circuit and adapted to be heated by the passage of the electric current.

2. The combination with an electric circuit of a closed chamber containing an expansible fluid, said chamber having an an nular transversely corrugated metal wall included in said circuit and adapted to be heated by the passage of the electric current.

3. The combination with an electric circuit of a closed chamber, forming a part of said circuit and containing an expansible fluid, said chamber comprising a bellows composed of a plurality of pairs of thin metal disks having central openings, the disks of each pair being connected together at their peripheries, and the adjacent disks of the several. pairs being connected at said openings by collars of metal of higher resistance than the metal in the disks.

4. A protective device for an electric circuit containing electric apparatus, comprising an expansible member, a quantity of iii) 

